Coral reefs face a multiplicity of threats from human activities. However, corals from the past bring a message of hope. Australian researchers have just established that these ecosystems have already withstood a dramatic environmental change: a drop in sea level of 120 meters!
Research on coral ecosystems in the past has shown that during periods of sea-level rise, corals are healthy and grow faster. Scientists have questioned the impact of the opposite phenomenon, sea level decline, on coral ecosystems. Such an environmental change is a priori more unfavorable to corals.
Of course, sea levels then were falling – and now they’re rising, but if we want to understand how corals react in hostile conditions, then we need to study what happens in all circumstances, says Pandolfi. When sea levels fall, there is a catastrophic reduction in coral habitats and a loss of connectivity between reefs. In fact, these conditions are similar in some ways to what corals are experiencing today as a result of human activities – so the parallels are useful.
Researchers at the University of Queensland’s ARC (Centre of Excellence for Coral Reef Studies) have been studying coral reefs from the last ice age when sea level fell 130 meters. That was in the Pleistocene, 20,000 years ago.
130 meters down? Not even scared!
Using data from eight fossil reefs in New Guinea, researchers have reconstructed the ecosystems of this particular period in their work published in the journal Ecology. Despite this dramatic change, the ecosystems have resisted well. While species composition has changed, coral diversity has been maintained, as has the variety of coral ecosystems. These coral reefs were then closer to the seabed, and their growth was slower.
Pleistocene corals prove the high resilience of corals to significant environmental pressures. However, it should not be forgotten that the current environmental changes, in their multiplicity and magnitude, are unprecedented.
Degradation of water quality, invasive species, bleaching, ocean acidification, rising water levels, and loss of habitats These are all phenomena that must be prevented or compensated for, according to John Pandolfi, to ensure that corals can emerge from the top of the 21st century’s climate change.